A requirement for a telescopic shaft of a steering mechanism unit of a vehicle includes absorbing an axis-directional displacement during vehicle travel so as to inhibit the transfer of the displacement and vibrations to a steering wheel. Further, another requirement includes a function of shifting a position of the steering wheel in an axis-direction and adjusting this position in order for a driver to obtain a position optimal for driving the vehicle.
In all these cases, the telescopic shaft is required to reduce backlash or rattling noises, a feeling of the backlash on the steering wheel, and slide resistance when sliding in the axis-direction.
Such being the case, a conventional contrivance is that metallic noises, metal butting noises, etc., are absorbed or reduced by coating a male shaft of the telescopic shaft with a nylon film and applying grease over a slide portion. Thus, the slide resistance and the backlash in a rotating direction are reduced.
There is, however, a case where abrasion of the nylon film progresses in the course of use, and the backlash in the rotating direction increases. Further, when exposed to a high temperature in an engine compartment, the nylon film suffers a volumetric change with the result being that the slide resistance conspicuously rises and the abrasion is highly accelerated, wherein the backlash in the rotating direction increases.
Under such circumstances, according to telescopic shafts disclosed in German Patent Publication DE3730393C2, Japanese Patent Application Laid-Open No. 2001-50293 and Japanese Patent Application Laid-Open No. 2001-193738, a rolling member and an preload elastic member, which preloads a male shaft and a female shaft, are interposed between an outer peripheral surface of the male shaft and an inner peripheral surface of the female shaft. With this configuration, when sliding, the elastic member preloads the rolling member against the female shaft to such an extent as not to cause backlash, whereby backlash between the male shaft and the female shaft can be prevented. Further, when transferring the torque, the elastic member can restrict the rolling member in a peripheral direction, and the male shaft and the female shaft can prevent backlash in the rotating direction thereof.
According to all these patent documents, however, the elastic member for preloading the rolling member and a race portion abutting on the rolling member are made from different materials and take different shapes for their usage.
This is because the race portion abutting on the rolling member must bear a high contact surface pressure. This implies that the torque must be transferred via the rolling member, and hence the race portion abutting on the rolling member is required to be a hard and rigid member. By contrast, the elastic member that generates a biasing force is required to be made from a flexible material, as in the case of a spring.
From these points described above, according to the patent document, i.e., German Patent Publication DE3730393C2, the race portion abutting on the rolling member involves using a different material and a different shape, and, as a result, it follows that manufacturing costs rise.
Moreover, German Patent Publication DE3730393C2 exemplifies an example of a plate spring, wherein the race portion and the elastic member are made from a single material. However, the plate springs are connected via a web, so that the configuration becomes complicated, resulting in a rise in assembling cost. Further, as described above, for transferring the torque through the rolling member, it is difficult to utilize the plate spring to bear the contact surface pressure of the rolling member and to give the biasing force.
Furthermore, Japanese Patent Application Laid-Open No. 2001-193738 exemplifies an example, wherein the elastic member and the race portion are integrally formed. As in the case described above, however, for transferring the torque via the rolling member, it is difficult to utilize the plate spring to bear the contact surface pressure of the rolling member and to give the biasing force.